One of the most common surfactants currently incorporated in detergent compositions is alkyl benzene sulphonate, particularly linear benzene sulphonate, herein referred to as LAS. The use of alkyl benzene sulphonate usually in combination with other anionic or nonionic surfactants has been found to give particularly effective cleaning performance, especially on greasy and oily stains over a wide range of temperatures and conditions.
It is also highly beneficial to incorporate enzymes into detergent compositions in order to improve overall performance. In particular lipases have been found to provide improvement in the removal of oily stains.
However, it is known from the art (for example EP 373 850) that lipases are particularly sensitive to the other ingredients in the composition in the wash liquor. In particular they are unstable in the presence of surface active agents. This problem is particularly acute in the presence of LAS, which has been shown to significantly reduce the activity of lipase.
Low LAS detergent compositions have been described in the art, for example in EP-A 544 490 and U.S. Pat. No. 4,260,529. However, such detergent compositions often have an low overall level of anionic surfactant which may result in a lower soil suspension capacity and less effective neutralisation of cationic fabric conditioners which may be present in the wash or on the fabric surface.
The art also describes the use of anionic surfactant based detergent compositions, preferably alkyl sulphate, comprising low levels of LAS. For example GB 1 399966 discloses detergent compositions comprising primary alcohol sulphate (PAS) and nonionic surfactants. EP-A 342 917 discloses detergent compositions comprising PAS having a range of chain lengths to improve the cleaning performance at lower temperatures. However, it has been observed that such detergent compositions do exhibit the same cleaning performance as the corresponding LAS compositions.
Therefore, it is an object of the present invention to replace the alkyl benzene sulphonate in surfactant systems with a surfactant which provides excellent cleaning benefits, giving similar overall performance compared to the alkyl benzene sulphonate surfactant systems and in the presence of which lipases are stable in the wash. In addition, another aim of the detergent manufactures is to develop a surfactant system which is readily biodegradable.
It has now been found that these objectives can be achieved by the use of a surfactant system comprising an alkyl alkoxylated sulphate having an average alkoxylation degree of from 0.1 to 10, having specific ratios of alkyl monoalkoxylated sulphate, alkyl dialkoxylated sulphate and alkyl alkoxylates sulphates with 3 or more alkoxy groups per alkyl group. It has been found that said alkyl alkoxy sulphates provide excellent cleaning benefits over a wide range of temperatures and show enhanced lipase stability.
Another advantage of the surfactant system of the present invention are the excellent wetting properties, which is a highly desirable property in detergent compositions.
Furthermore, the surfactant systems of the present invention is particularly efficient in the removal of oily stains.
Detergent compositions comprising alkyl ethoxy sulphates (referred to herein as AES) and lipases have been described in various contexts in the art. For example WO 92/06158 discloses detergent compositions comprising AES with an ethoxylation degree greater than 0, comprising lipases. U.S. patent application Ser. No. 92 05659 discloses detergent compositions comprising AES with a preferred average ethoxylation of from 0.5 to 2. Lipases are mentioned. European Patent Application number 907159.3 discloses granular detergent compositions comprising AES with an ethoxylation degree of 1 to 7. Lipases are disclosed.
JP 4072395 discloses a liquid detergent composition comprising alkyl/alkenyl sulphates having an average ethoxylation of 1 to 7 and enzymes. JP 1161096 discloses a detergent composition comprising alkenyl ether sulphates having from 0.5 to 8 ethoxylation, alkyl sulphates, LAS and lipases.
However, none of the identified art recognise the performance benefits associated with anionic surfactant systems comprising alkyl alkoxylated sulphates having specific ratios of mono-, di- and trialkoxylated sulphates in combination with lipases as in the present invention.